Microbial communities and functional genes of nitrogen cycling in an electrolysis augmented constructed wetland treating wastewater treatment plant effluent

To enhance nitrogen removal efficiency, a new electrolysis augmented constructed wetland (E-CW) was applied for nitrogen removal from waste water treatment plant (WWTP) effluent. This work demonstrated that E-CW could remove NO3− efficiently (45.5%-83.4%) under low CCOD/N ratio (average 2.29 ± 0.45) with little amount of NH4+ and NO2− generation. High throughput 16S rRNA sequence analysis revealed that Proteobacteria, Actinobacteria, Cyanobacteria, Bacteroidetes, and Verrucomicrobia were the dominant phyla in the E-CW. However, abundance of denitrifiers and denitrification genes decreased along with the operation of E-CW. Four functional gene pairs of anammox-amoA, (narG + napA)-(nirK + nirS), (narG + napA)-nosZ and qnorB-nosZ showed positive correlations with each other. Co-occurrence network analysis results indicated that functional guilds of FeOB and FeRB coupled with denitrifiers and contributed to the process of nitrogen removal in the E-CW. Overall, this work illustrated E-CW was a feasible and effective technology for enhancing nitrogen removal, and provided a theoretical basis for better design and operation of E-CW.